This project generated 14 publications (6 in refereed journals, one book chapter, and 7 in conference proceedings) during the past year, in addition to 7 papers that have been submitted for publication in refereed journals. We can define six main areas of research progress: (1) nonlinear modeling of physiological systems; (2) nonstationary modeling of nonlinear physiological systems; (3) nonlinear modeling with point-process input data; (4) decomposition of nonlinear feedback via adaptive estimation; (5) nonlinear parametric models from nonparametric measurements; and (6) laser-induced fluorescence spectroscopy Of particular importance are the general methodologies that yield compact nonlinear and nonstationary models within the practical limitations of experimental investigations, solving a long-standing problem of critical importance for physiological system modeling. Pilot applications to experimental data from the rat kidney, spider mechanoreceptors and the rabbit hippocampus have yielded new insights into the physiological mechanisms of these systems.